--- 1/draft-ietf-tcpm-experimental-options-04.txt 2013-03-13 20:00:27.439771217 +0100 +++ 2/draft-ietf-tcpm-experimental-options-05.txt 2013-03-13 20:00:27.459709525 +0100 @@ -1,17 +1,17 @@ TCPM Working Group J. Touch Internet Draft USC/ISI -Intended status: Proposed Standard February 25, 2013 -Expires: August 2013 +Intended status: Proposed Standard March 13, 2013 +Expires: September 2013 Shared Use of Experimental TCP Options - draft-ietf-tcpm-experimental-options-04.txt + draft-ietf-tcpm-experimental-options-05.txt Status of this Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. @@ -20,21 +20,21 @@ months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html - This Internet-Draft will expire on August 25, 2013. + This Internet-Draft will expire on September 13, 2013. Copyright Notice Copyright (c) 2013 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents @@ -51,30 +51,31 @@ same connection. It uses a new IANA TCP experiment identifier, and is also robust to experiments that are not registered and those that do not use this sharing mechanism. It is recommended for all new TCP options that use these codepoints. Table of Contents 1. Introduction...................................................2 2. Conventions used in this document..............................4 3. TCP Experimental Option Structure..............................4 - 3.1. Selecting an ExID.........................................5 - 3.2. Impact on TCP Option Processing...........................6 - 4. Reducing the Impact of False Positives.........................6 - 5. Migration to Assigned Options..................................7 - 6. Security Considerations........................................7 - 7. IANA Considerations............................................7 - 8. References.....................................................8 - 8.1. Normative References......................................8 - 8.2. Informative References....................................8 - 9. Acknowledgments................................................9 + 3.1. Selecting an ExID.........................................6 + 3.2. Impact on TCP Option Processing...........................7 + 4. Reducing the Impact of False Positives.........................7 + 5. Migration to Assigned Options..................................8 + 6. Rationale......................................................8 + 7. Security Considerations........................................9 + 8. IANA Considerations............................................9 + 9. References....................................................10 + 9.1. Normative References.....................................10 + 9.2. Informative References...................................10 + 10. Acknowledgments..............................................11 1. Introduction TCP includes options to enable new protocol capabilities that can be activated only where needed and supported [RFC793]. The space for identifying such options is small - 256 values, of which 30 are assigned at the time this document was published [IANA]. Two of these codepoints are allocated to support experiments (253, 254) [RFC4727]. These values are intended for testing purposes or anytime an assigned codepoint is either not warranted or available, e.g., @@ -188,51 +189,93 @@ 0 1 2 3 01234567 89012345 67890123 45678901 +--------+--------+--------+--------+ | Kind | Length | ExID | +--------+--------+--------+--------+ | ExID (con't) | option contents... +--------+--------+--------+--- Figure 3 TCP Experimental Option with a 32-bit ExID + This mechanism is encouraged for all TCP options that are not yet + eligible for assigned codepoints: + >> Protocols requiring new TCP option codepoints that are not eligible for assigned values SHOULD use the existing TCP experimental option codepoints (253, 254) with ExIDs as described in this document. + This mechanism is encouraged for all TCP options using the current + experimental codepoints in controlled environments: + >> All protocols using the TCP experimental option codepoints (253, - 254) SHOULD use ExIDs as described in this document. + 254), even those deployed in controlled environments, SHOULD use + ExIDs as described in this document. + + This mechanism is required for all TCP options using the current + experimental codepoints that are publicly deployed, whether enabled + by default or not: + + >> All protocols using the TCP experimental option codepoints (253, + 254) that are deployed outside controlled environments, such as in + the public Internet, MUST use ExIDs as described in this document. + + Once a TCP option uses the mechanism in this document, registration + of the ExID with IANA is required: + + >> All protocols using ExIDs as described in this document MUST + register those ExIDs with IANA. + + Applicants register their desired ExID by contacting IANA [IANA]. 3.1. Selecting an ExID ExIDs are selected at design time, when the protocol designer first implements or specifies the experimental option. ExIDs can be either 16-bits or 32-bits. In both cases, the value is stored in the header in network-standard (big-endian) byte order. ExIDs combine properties of IANA registered codepoints with "magic numbers". + >> All ExIDs MUST be either 16-bits or 32-bits long. + + Use of the ExID, whether 16-bit or 32-bit, helps reduce the + probability of a false positive collision with those who either do + not register their experiment or who do not implement this + mechanism. + ExIDs are registered with IANA using "first-come, first-served" priority based on the first two bytes. Those two bytes are thus sufficient to interpret which experimental option is contained in the option field. + >> All ExIDs MUST be unique based on their first 16 bits. + The second two bytes serve as a "magic number". A magic number is a self-selected codepoint whose primary value is its unlikely collision with values selected by others. Magic numbers are used in - other protocols, e.g., BOOTP [RFC951] and DHCP [RFC2131]. The magic - number helps reduce the probability of a false positive collision - with those who either do not register their experiment or who do not - implement this mechanism. Using the additional magic number bytes - also helps the option contents have the same byte alignment in the - TCP header as they would have if (or when) a conventional (non- - experiment) TCP option codepoint is assigned. + other protocols, e.g., BOOTP [RFC951] and DHCP [RFC2131]. + + Using the additional magic number bytes helps the option contents + have the same byte alignment in the TCP header as they would have if + (or when) a conventional (non-experiment) TCP option codepoint is + assigned. Use of the same alignment reduces the potential for + implementation errors, especially in using the same word-alignment + padding, if the same software is later modified to use a + conventional codepoint. Use of the longer, 32-bit ExID further + decreases the probability of such a false positive compared to those + using shorter, 16-bit ExIDs. + + Use of the ExID does consume TCP option space but enables concurrent + use of the experimental codepoints and provides protection against + false positives, leaving less space for other options (including + other experiments). Use of the longer, 32-bit ExID consumes more + space, but provides more protection against false positives. 3.2. Impact on TCP Option Processing The ExID number is considered part of the TCP option, not the TCP option header. The presence of the ExID increases the effective option Length field by the size of the ExID. The presence of this ExID is thus transparent to implementations that do not support TCP options where it is used. During TCP processing, ExIDs in experimental options are matched @@ -257,22 +300,22 @@ these are experiments, neither consideration is a substantial impediment; a finalized protocol can avoid both issues with the assignment of a dedicated option codepoint later. 4. Reducing the Impact of False Positives False positives occur where the ExID of one experiment matches the value of an option that does not use ExIDs or if two experiments select the same ExID. Such collisions can cause an option to be interpreted by the incorrect processing routine. Use of checksums or - signatures may help an experiment use a shorter ExID while reducing - the corresponding increased potential for false positives. + signatures may help an experiment use the shorter ExID while + reducing the corresponding increased potential for false positives. >> Experiments that are not robust to ExID false positives SHOULD implement other detection measures, such as checksums or minimal digital signatures over the experimental options they support. 5. Migration to Assigned Options Some experiments may transition from experiment, and become eligible for an assigned TCP option codepoint. This document does not recommend a specific migration plan to transition from use of the @@ -298,96 +341,164 @@ >> A TCP segment MUST NOT contain both an assigned TCP option codepoint and a TCP experimental option codepoint for the same protocol. Instead, a TCP that intends backward compatibility might send multiple SYNs with alternates of the same option and discard all but the most desired successful connection. Although this approach may resolve more slowly or require additional effort at the endpoints, it is preferable to excessively consuming TCP option space. -6. Security Considerations +6. Rationale + + The ExIDs described in this document combine properties of IANA + first-come/first-served (FCFS) registered values with magic numbers. + Although IANA FCFS registries are common, so too are those who + either fail to register or who 'squat' by deliberately using + codepoints that are assigned to others. The approach in this + document is intended to recognize this reality and be more robust to + its consequences than would be a conventional IANA FCFS registry. + + Existing ID spaces were considered as ExIDs in the development of + this mechanism, including IEEE Organizationally Unique Identifier + (OUI) and IANA Private Enterprise Numbers (PENs) [802] [OUI] + [RFC1155]. + + OUIs are 24-bit identifiers that are combined with 24 to 40-bits of + privately-assigned space to create identifiers that commonly + assigned to a unique piece of hardware. OUIs are already longer than + the smaller ExID value, and obtaining an OUI is costly (currently + $1,885.00 USD). An OUI could be obtained for each experiment, but + this could be considered expensive. An OUI already assigned to an + organization could be shared if extended (to support multiple + experiments within an organization), but this would either require + coordination within an organization or an IANA registry; the former + is prohibitive, and the latter is more complicated than to have IANA + manage the entire space. + + PENs were originally used in SNMP [RFC1157]. PENs are identifiers + that can be obtained without cost from IANA [PEN]. Despite the + current registry, the size of the PEN assignment space is currently + undefined, and has only recently been proposed (as 32-bits) [Li12]. + PENs are currently assigned to organizations, and there is no + current process for assigning them to individuals. Finally, if 32- + bits as expected, they would be larger than needed in many cases. + +7. Security Considerations The mechanism described in this document is not intended to provide (nor does it weaken existing) security for TCP option processing. -7. IANA Considerations +8. IANA Considerations This document calls for IANA to create a new TCP experimental option - Experiment Identifier (ExID) registry. + Experiment Identifier (ExID) registry. The registry records both 16- + bit and 32-bit ExIDs, as well as a name and e-mail contact for each + entry. - That registry should allow 16-bit and 32-bit entries, where entries - are "first-come, first-served" on the first two bytes of the value - in network-standard byte order (big endian), in which the entry - should indicate the entire ExID value. Known overlapping uses - - whether of the first-come portion or the entire value - should also - be listed and highlighted as collisions. + Entries are assigned on a First-Come, First-Served (FCFS) basis + [RFC5226]. The registry operates FCFS on the first two bytes of the + ExID (in network-standard order) but records the entire ExID (in + network-standard order). Some examples are: + + o 0x12340000 collides with a previous registration of 0x1234abcd + + o 0x5678 collides with a previous registration of 0x56780123 + + o 0xabcd1234 collides it a previous registration of 0xabcd + IANA will advise applicants of duplicate entries to select an + alternate value, as per typical FCFS processing. + + IANA will record known duplicate uses to assist the community in + both debugging assigned uses as well as correcting unauthorized + duplicate uses. IANA should impose no requirements on making a registration other than indicating the desired codepoint and providing a point of contact. A short description or acronym for the use is desired, but should not be required. -8. References +9. References -8.1. Normative References +9.1. Normative References [RFC793] Postel, J., "Transmission Control Protocol", STD 7, RFC 793, Sep. 1981. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC4727] Fenner, B., "Experimental Values in IPv4, IPv6, ICMPv4, ICMPv6, UDP, and TCP Headers", RFC 4727, Nov. 2006. -8.2. Informative References + [RFC5226] Narten, T., H. Alvestrand, "Guidelines for Writing an IANA + Considerations Section in RFCs", BCP 26, RFC 5226, May + 2008. + +9.2. Informative References + + [802] "IEEE Standard for Local and Metropolitan Area Networks: + Overview and Architecture", IEEE 802-2001, 8 March 2002. [Bi11] Bittau, A., D. Boneh, M. Hamburg, M. Handley, D. Mazieres, Q. Slack, "Cryptographic protection of TCP Streams (tcpcrypt)", work in progress, draft-bittau-tcp-crypt-03, Sep. 3, 2012. [Ed11] Eddy, W., "Additional TCP Experimental-Use Options", work in progress, draft-eddy-tcpm-addl-exp-options-00, Aug. 16, 2011. [IANA] IANA web pages, http://www.iana.org/ + [Li12] Liang, P., A. Melnikov, "Private Enterprise Number (PEN) + practices and Internet Assigned Numbers: Authority (IANA) + considerations for registration procedures", draft-liang- + iana-pen-01, (work in progress), June 2012. + + [OUI] IEEE OUI registry, + http://standards.ieee.org/develop/regauth/oui/ + + [PEN] IANA Private Enterprise Numbers, + http://www.iana.org/assignments/enterprise-numbers + [RFC951] Croft, B., J. Gilmore, "BOOTSTRAP PROTOCOL (BOOTP)", RFC 951, Sept. 1985. + [RFC1155] Rose, M., K. McCloghrie, "Structure and Identification of + Management Information for TCP/IP-based internets", RFC + 1155, May 1990. + + [RFC1157] Case, J., M. Fedor, M. Schoffstall, J. Davin, "A Simple + Network Management Protocol (SNMP)", RFC 1157, May 1990. + [RFC2026] Bradner, S., "The Internet Standards Process -- Revision 3", BCP 9, RFC 2026, Oct. 1996. [RFC2131] Droms, R., "Dynamic Host Configuration Protocol", RFC 2131, Mar. 1997. [RFC2780] Bradner, S., V. Paxson, "IANA Allocation Guidelines For Values In the Internet Protocol and Related Headers", BCP 37, RFC 2780, Mar. 2000. [RFC3692] Narten, T., "Assigning Experimental and Testing Numbers Considered Useful", BCP 82, RFC 3692, Jan. 2004. - [RFC5226] Narten, T., H. Alvestrand, "Guidelines for Writing an IANA - Considerations Section in RFCs", BCP 26, RFC 5226, May - 2008. - [RFC6013] Simpson, W., "TCP Cookie Transactions (TCPCT)", RFC 6013, Jan. 2011. [Si11] Simpson, W., "TCP Cookie Transactions (TCPCT) Sockets Application Program Interface (API)", work in progress, draft-simpson-tcpct-api-04, Apr. 7, 2011. -9. Acknowledgments +10. Acknowledgments This document was motivated by discussions on the IETF TCPM mailing list and by Wes Eddy's proposal [Ed11]. Yoshifumi Nishida, Pasi Sarolathi, and Michael Scharf provided detailed feedback. This document was prepared using 2-Word-v2.0.template.dot. Authors' Addresses Joe Touch